Microsoft Office on the iPad, in what is more likely a case of "not if, but when." (Credit: CNET TV)

Microsoft could be leaving as much as $2.5 billion on the table by failing to get a version of Office for iPhones and iPads out the door, according to Morgan Stanley analyst Adam Holt.

The Redmond, Wash.-based software giant already has some software available for the iPhone and iPad in the pipeline—but as with Office, they have yet to make an appearance. It's now at the point where even Microsoft are "no longer bothering" to deny the rumors," according to ZDNet's Mary Jo Foley, but the company is far from being forthcoming about an expected release date or in what form a release may take.

According to Holt in a note to investors, he said that Microsoft could generate a greater return on Office, by as much as close to half of what Office earns today. $2.5 billion, in fact.

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Holt estimates that if it were to release Office for iOS for around $60, just shy of one-third of iPad users would snap up the software. Should the current iPad cumulative sales trend continue to 200 million by the end of 2014, Holt believes that Microsoft could generate around $2.5 billion in revenue on Office for iPad alone, after Apple collects its commission fees, of course.

Holt also adds that around 30-40 percent of Mac users install paid versions of Office 2008/2011 as Windows PC users do. The figure is a bit skewed, considering that some Windows machines come with a basic version of Office already installed.

"The math is compelling, and may drive Microsoft to move Office," he wrote.

It's a rough estimate, but it's more of a point to show that not only Microsoft generate vast sums more in its Office business than it does now, but also that Apple could end up capitalizing on Microsoft's expected runaway success with the mobile software.

But here's where it gets even more interesting. Microsoft may not pay that 30 percent fee to Apple, by circumventing the need to go through the iPhone and iPad's app store altogether.

One of the problems with bringing Microsoft software to iPhone and iPad is that Apple will receive a 30 percent cut of every sale. Many Microsoft apps are available for iPhone and iPad already—not limited to OneNote, SkyDrive and Lync—and are free to download, so the company avoids paying a 30 percent cut to Apple.

But bringing Office to the iPad could ultimately lead to the death throes of Microsoft's own strategy, notably with Surface—which remains the only tablet on the market with a 'legitimate' (used carefully, granted) version of Office installed.

Office for iPhone or iPad may seem frivolous to some, but it's an important bridge for bring-your-own-device (BYOD) users as well as ordinary enterprise users alike.

The majority of businesses still rely on Microsoft Office—in whatever incarnation, including partially Web-based Office 365—and iPad remains popular in the enterprise thanks to its back-end mobile device policy management.